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Method and apparatus for providing improved pinning structure for tunneling magnetoresistive sensorMethod and apparatus for providing improved pinning structure for tunneling magnetoresistive sensor description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070188938, Method and apparatus for providing improved pinning structure for tunneling magnetoresistive sensor. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention relates in general to magnetic read sensors, and more particularly to a method and apparatus for providing improved pinning structure for tunneling magnetoresistive sensor. [0003] 2. Description of Related Art [0004] The heart of a computer is typically a magnetic disk drive which includes a rotating magnetic disk, a slider that has write and read heads, a suspension arm above the rotating disk and an actuator arm. The suspension arm biases the slider into contact with a parking ramp or the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the actuator arm swings the suspension arm to place the write and read heads over selected circular tracks on the rotating disk where field signals are written and read by the write and read heads. The write and read heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions. [0005] Most "giant magnetoresistive" (GMR) devices have been designed so as to measure the resistance of the free layer for current flowing parallel to the film's plane. However, as the quest for ever greater densities continues, devices that measure current flowing perpendicular to the plane (CPP) have begun to emerge. A device that is particularly well suited to the CPP design is the magnetic tunneling junction (MTJ) in which the layer that separates the free and pinned layers is a non-magnetic insulator, such as alumina or silica. Its thickness needs to be such that it will transmit a significant tunneling current. The principle governing the operation of the MTJ is the change of resistivity of the tunnel junction between two ferromagnetic layers. When the magnetization of the two ferromagnetic layers is in opposite directions, the tunneling resistance increases due to a reduction in the tunneling probability. [0006] A sensor includes a nonmagnetic electrically conductive or electrically nonconductive material spacer layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer typically interfaces the pinned layer for pinning the magnetic moment of the pinned layer 90.degree to an air bearing surface (ABS) wherein the ABS is an exposed surface of the sensor that faces the rotating disk. The sensor is located between ferromagnetic first and second shield layers. [0007] A magnetic moment of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative magnetic field signals from the rotating magnetic disk. The quiescent position of the magnetic moment of the free layer, which is parallel to the ABS, is when the current is conducted through the sensor without magnetic field signals from the rotating magnetic disk. [0008] When the free layer is exposed to an external magnetic field, the direction of its magnetization is free to rotate according to the direction of the external field. After the external field is removed, the magnetization of the free layer will stay at a direction, which is dictated by the minimum energy state, determined by the crystalline and shape anisotropy, current field, coupling field and demagnetization field. If the direction of the pinned field is parallel to the free layer, electrons passing between the free and pinned layers, suffer less scattering. Thus, the resistance at this state is lower. If, however, the magnetization of the pinned layer is anti-parallel to that of the free layer, electrons moving from one layer into the other will suffer more scattering so the resistance of the structure will increase. [0009] Sensors can also be categorized as current in plane (CIP) sensors or as current perpendicular to plane (CPP) sensors. In a CIP sensor, current flows from one side of the sensor to the other side parallel to the planes of the materials making up the sensor. Conversely, in a CPP sensor the sense current flows from the top of the sensor to the bottom of the sensor perpendicular to the plane of the layers of material making up the sensor. [0010] In order to increase data density and data rate even further, in recent years researchers have focused on the use of tunnel junction (TMR) sensors or tunnel valve. A TMR read sensor is similar in structure to a "giant magnetoresistive" (GMR) spin valve, but the physics of the device are different. For a TMR read sensor, rather than using a spacer layer, a barrier layer is positioned between the free layer and a synthetic antiferromagnet (SAF). Electrons must tunnel through the barrier layer. A tunnel valve operates based on quantum mechanical tunneling of electrons through the insulating spacer layer. This tunneling is maximized when the magnetizations of the free and pinned layers are parallel to one another adjacent to the spacer layer. [0011] Both GMR sensors and TMR sensors require a mechanism for maintaining the pinned layer in its pinned state. Traditionally, this has been achieved by depositing the pinned layer such that it is exchange coupled with an antiferromagnetic material such as for example PtMn. Although an antiferromagnetic material in and of itself is not magnetic, when exchange coupled with a magnetic material it very strongly fixes the magnetization of the magnetic layer, In order to effectively fix the magnetization of the pinned layer, the antiferromagnetic layer must be very thick as compared with the other layers of the sensor. Ever increasing recording density requirements require ever smaller gap height and therefore thinner sensors. The thick AFM layer is a significant cost to the thickness budget. Also, antiferromagnetic materials lose their antiferromagnetic properties at a given temperature called the blocking temperature. Therefore, certain events such as an electrostatic discharge or a slider contacting the disk can elevate the temperature of the AFM sufficiently to lose the pinning of the pinned layer. Such an event renders the head useless. [0012] In order to further improve pinning of the pinned layer, heads have recently been constructed with anti-parallel coupled pinned layers (AP coupled pinned layers). In such a sensor the pinned layer consists of a pair of ferromagnetic layers separated by a non-magnetic coupling layer such as Ru. The ferromagnetic layers are usually constructed to have magnetic thicknesses that are close to each other but not exactly the same. The antiparallel magnetostatic coupling of the two ferromagnetic layers greatly increases the pinning, and the slight difference in magnetic thicknesses creates a net magnetism that allows magnetic orientation of the AP coupled pinned layer to be set in a magnetic field. In such an AP coupled pinned layer, the ferromagnetic layer furthest from the sensor's spacer layer is exchange coupled with an AFM as discussed in the preceding paragraph. [0013] Even more recently, in order to minimize sensor height and thereby increase data density, attempts have been made to construct sensors in which the pinned layer does not require exchange coupling to an AFM. In such a sensor, two antiparallel coupled ferromagnetic layers are constructed to have as close as possible a magnetic thickness. The closer the magnetic thickness, the stronger the magnetostatic coupling between the layers. The antiparallel coupled layers are also constructed of a material having a strong positive magnetostriction. Magnetostriction is the property of a material that it is magnetized in a particular direction when placed under a compressive stress. The construction of the head generates a certain amount of compressive stress on the sensor which, when combined with the magnetostriction of the pinned layers, assists pinning. Such self-pinned sensors have shown promise in greatly decreasing the thickness of the sensor, however they suffer from instability. The pinned layers of such sensor have been prone to flip direction, a catastrophic event that renders the head useless. [0014] In particular, a TMR sensor that uses CoFeB amorphous layer as the reference layer in conjunction with MgO as the barrier layer has shown an improved TMR ratio. The sensitivity to the magnetic data is measured in the TMR ratio, defined as the ratio between the resistivity values with and without a magnetic field. More particularly, the resistance change rate (TMR ratio; ..DELTA.R.sub.TMR) of the tunneling magnetoresistive sensor is expressed by 2P.sub.PP.sub.F/(1-P.sub.PP.sub.F). Herein, P.sub.P represents a spin polarization rate (i.e., difference in the number of electrons between upward spins and downward spins, which is normalized based on the total number of electrons; referred to simply as a "polarization rate" hereinafter) of the pinned magnetic layer. P.sub.F represents a polarization rate of the free magnetic layer. As seen from that formula, the resistance change rate is determined depending on-the polarization rate of the ferromagnetic layer. Theoretically, the resistance change rate is increased as the polarization rate increases. However, a CoFeB amorphous layer has a large magnetostriction constant, which is undesirable for pinning. [0015] It can be seen then that there is a need for a method and apparatus for providing improved pinning structure for tunneling magnetoresistive sensor. SUMMARY OF THE INVENTION [0016] To overcome the limitations described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for providing improved pinning structure for tunneling magnetoresistive sensor. [0017] The present invention solves the above-described problems by using a three layer pinning structure wherein the second pinned layer is designed to balance the effects of the first and third pinned layers. [0018] A read sensor in accordance with the principles of the present invention includes an antiferromagnetic layer, a pinned layer, the pinned layer further including a first, second and third antiparallel layer, a free layer and a barrier layer disposed between the free layer and the pinned layer, wherein the first antiparallel layer includes a composition selected to maximize coupling with the antiferromagnetic layer, the third antiparallel layer includes a composition selected to maximizes a Tunnel-Magnetoresistance, and wherein the second antiparallel layer is disposed between the first and third antiparallel layers and includes a composition selected to balance the stressed induced anisotropy of the first and third antiparallel layers. [0019] In another embodiment of the present invention, a magnetic storage device is provided. The magnetic storage device includes a magnetic media for storing data thereon, a motor, coupled to the magnetic media, for translating the magnetic media, a transducer for reading and writing data on the magnetic media and an actuator, coupled to the transducer, for moving the transducer relative to the magnetic media, wherein the transducer includes a read sensor including an antiferromagnetic layer, a pinned layer, the pinned layer further including a first, second and third antiparallel layer, a free layer and a barrier layer disposed between the free layer and the pinned layer, wherein the first antiparallel layer includes a composition selected to maximize coupling with the antiferromagnetic layer, the third antiparallel layer includes a composition selected to maximizes a Tunnel-Magnetoresistance, and wherein the second antiparallel layer is disposed between the first and third antiparallel layers and includes a composition selected to balance the stressed induced anisotropy of the first and third antiparallel layers. [0020] In another embodiment of the present invention, a method for forming a read sensor is provided. The method for forming a read sensor includes forming a pinning layer, forming a pinned layer having a first, second and third antiparallel layer abutting the pinning layer, wherein the design of the second layer, disposed between the first and third antiparallel layers, is selected to maximize tunnel-magnetoresistance and pinning while minimizing sensitivity to external stress, forming a barrier layer abutting the pinned layer and forming a free layer abutting the barrier layer. [0021] These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention. BRIEF DESCRIPTION OF THE DRAWINGS Continue reading about Method and apparatus for providing improved pinning structure for tunneling magnetoresistive sensor... Full patent description for Method and apparatus for providing improved pinning structure for tunneling magnetoresistive sensor Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method and apparatus for providing improved pinning structure for tunneling magnetoresistive sensor patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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